1. Field of the Invention
The present invention relates in general to a vibration type actuator drive controller, and more particularly to a vibration type actuator drive controller and a method of controlling a drive speed of a vibration type actuator adapted to excite a vibration member by applying an A.C. signal to an electromechanical energy transducer to obtain a driving force.
2. Related Background Art
In a vibration type actuator adapted to excite a vibration member by applying an A.C. signal to an electromechanical energy transducer to obtain a driving force, heretofore, various proposals have been made for an acceleration/deceleration method for a vibration type motor which is one of vibration type actuators.
For example, Japanese Patent Application Laid-Open No. H06-269182 discloses a technique in which to stably accelerate and decelerate a vibration type motor, characteristics of the vibration type motor, especially, gradients of a drive speed with respect to a drive frequency of the vibration type motor are learnt in advance, and an operation for updating the drive frequency is repeatedly carried out as may be necessary by utilizing the gradients thus learnt. Thus, the smooth and stable control for start and stop of the vibration type motor can be conducted irrespective of the fluctuation in characteristics.
U.S. Pat. No. 5,644,199 also discloses a technique in which to drive a vibration type motor stably and efficiently in starting and stopping the vibration type motor without generating an abnormal sound and vibrations, a frequency of an A.C. voltage to be applied to a vibration member is variably controlled in a region of a frequency higher than a resonance frequency of the vibration member (in a region where a gradient of a drive speed with respect to the drive frequency is negative), and in starting the vibration type motor, the frequency of the A.C. voltage applied to the vibration member is swept from a high frequency to a low frequency in the frequency region concerned to accelerate the vibration type motor. Then, in decelerating the vibration type motor to stop the vibration type motor, the frequency of the A.C. voltage applied to the vibration member is swept from the frequency at that time to a high frequency in the frequency region concerned to gradually decrease the motor drive speed to stop the motor.
Moreover, with this technique, in a controller for the vibration type motor which is configured so that a speed of the vibration type motor becomes a predetermined value in accordance with speed feedback control, in starting the vibration type motor, a target speed data of which is sent from a microcomputer or the like to the controller is gradually increased for acceleration, and in stopping the vibration type motor, the target speed is gradually decreased for deceleration to thereby prevent an abnormal sound from being generated in stopping as well as in starting the vibration type motor. Further, a drive frequency may undergo the feedback control in a state where the drive frequency is made lower than a resonance frequency of a vibration member due to a start delay resulting from a mechanical time constant of a system having the vibration type motor and a load to which the vibration type motor is connected, and as a result, the vibration type motor may be stopped in some cases. However, such a situation is prevented in the above-mentioned vibration type motor controller.
In the invention disclosed in Japanese Patent Application. Laid-Open No. H06-269182, however, a preliminary operation is required since the gradients of the drive speed with respect to the drive frequency must be learnt in advance. Also, since the stored gradient information strictly changes if there is a fluctuation in environmental conditions such as a temperature, it is difficult to carry out an acceleration operation usually under the same progress. In particular, in an apparatus which is configured so that a vibration type motor and another actuator operate in conjunction with each other, there is a possibility that an operational difference may be generated therebetween and hence nonconformity may be generated in an operation of the apparatus. Moreover, there is encountered a problem that since means for storing information of gradients is required, the apparatus becomes expensive, and so forth.
In addition, in the invention disclosed in U.S. Pat. No. 5,644,199, since the frequency of the A.C. voltage to be applied to the vibration type motor is swept without detecting a drive speed of the vibration type motor, a difference is generated in the acceleration operation due to a fluctuation in environmental conditions such as a temperature or in a load state. Thus, similarly to the above-mentioned problem associated with the invention disclosed in Japanese Patent Application Laid-Open No. H06-269182, there is a possibility that nonconformity may be generated in an apparatus which is configured so that the vibration type motor and another actuator operate in conjunction with each other.
Moreover, in the above-mentioned conventional method of gradually changing the target speed the data of which is sent from the microcomputer or the like to the controller, since the microcomputer operates in accordance with a software, a high speed timing at which the data of the target speed is sent can not be made. For this reason, the acceleration operation and the deceleration operation can not be smoothly carried out. In addition, there is also encountered a problem that the control circuit is expensive.